The invention relates to a method for joining extruded plastic monofilaments at the circumferential surfaces thereof wherein the monofilaments, following extension, are stretched and subsequently stabilized. The invention is also directed at a method for marking and/or structurally changing or modifying such monofilaments or individual monofilaments of this kind within a monofilament group.
Monofilaments are produced by extrusion from virtually random polymers. Extrusion takes place with cross-sections adapted to the subsequent use of the monofilament. Thus, it is possible to produce extremely thin fibers, bristles and strands. The term xe2x80x9cmonofilamentsxe2x80x9d is understood to mean all continuously extruded monofilaments with diameters ranging from fibers to bristles for industrial purposes, even though subsequently, in exemplified manner, reference is mainly made to bristles.
In many cases there is a need for bristle material of monofilaments with different characteristics. The provision of bristles formed from two or more monofilaments has hitherto been unsuccessful in that multicore bristles could only be produced by adhesion or coating in an inadequate manner and only accompanied by a loss of their characteristics. Multicore, twisted bristles, during use and at least at the ends, have undesirably separated again. Integrally or positively engaging connections between several, initially individually extruded monofilament cores have not hitherto existed.
There is a special need for bristles formed from monofilament cores of different types. The combination of monofilament cores, e.g. from hard thermoplastics and soft elastomers leads to new effects. This also applies regarding the combination of monofilament cores with abrasive and non-abrasive action. Combined bristle actions more particularly result from the combination of monofilament cores of different cross-sections such as e.g. the connection of round and polygonal or otherwise profiled monofilament cores. In many cases the effects can be increased, if other monofilament cores are wound in spiral or crossing, wide or narrow-meshed manner around one or more axially positioned monofilament cores. In place of encircling, it is also possible to use other entwining methods.
The problem of the invention is therefore to join monofilaments of optionally differing polymers during or after extrusion so as to form a monofilament union.
According to the invention, this problem is solved in that monofilaments with different absorption coefficients for laser beams (LS) are used and at least zonally contacted at the circumferential surface thereof and by the introduction of laser beams into the contact area are melted together or positively joined, wherein introduction of the laser radiation occurs prior to stretching and/or following stretching, and/or following stabilization.